The proposed research continues investigations of the dynamics of molecular processes which occur on the surface membranes of animal cells. Its purpose is to understand the molecular mechanisms of control of growth, differentiation and function of normal and cancer cells. Measurements by fluorescence photobleaching recovery of lateral molecular motion by diffusion and cooperative driven flow of fluorescence labeled proteins and lipid analogs are emphasized. Of particular concern is regulation of mobility by coupling with the cytoskeleton. Current projects include (1) measurements of the restriction by the cytoskeleton of receptor and antigen mobility on lymphocytes and acetylcholine receptor on myotubes, (2) mobility and clustering of the receptor for low density lipoprotein, (3) modulation of mobility by Con A platelets, (4) assembly of viruses in and on cells and (5) effects of cholesterol on protein mobility. New techniques for topographical analysis of motility and cooperative motion of fluorescence labeled molecules on the cell surface using video image acquisition and analysis are being developed and applied.